Bone anchors with longitudinal connecting member engaging inserts and closures for fixation and optional angulation

ABSTRACT

Polyaxial bone anchors include a retainer for holding a shank within a receiver, the retainer being in at least two discrete pieces and cooperating with a variety of inserts, some of which independently lock the polyaxial mechanism. Polyaxial and mono-axial bone anchor assemblies include pivot and/or pressure inserts or pads that cooperate with longitudinal connecting members to provide a desired degree of continued control of angulation of the longitudinal connecting member in the sagittal plane or to hold the connecting member in place. Pressure pads for deformable rods may also be made from a deformable plastic material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/804,999, filed Aug. 3, 2012 which claimed the benefit of U.S.Provisional Patent Application Ser. No. 61/273,399, filed Aug. 4, 2009,the disclosure of both of which are incorporated by reference herein.U.S. patent application Ser. No. 12/804,999 was also acontinuation-in-part of U.S. patent application Ser. No. 12/080,202filed Apr. 1, 2008 that is a continuation-in-part of U.S. patentapplication Ser. No. 11/281,818 filed Nov. 17, 2005, now U.S. Pat. No.7,625,396, that claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/630,478 filed Nov. 23, 2004, all of thedisclosures of which are incorporated by reference herein. U.S. patentapplication Ser. No. 12/804,999 was also a continuation-in-part of U.S.patent application Ser. No. 12/229,207 filed Aug. 20, 2008 that claimsthe benefit of U.S. Provisional Patent Application Ser. No. 60/994,083filed Sep. 17, 2007 and was a continuation-in-part of U.S. patentapplication Ser. No. 11/522,503 filed Sep. 14, 2006 that is acontinuation-in-part of U.S. patent application Ser. No. 11/024,543filed Dec. 20, 2004, now U.S. Pat. No. 7,204,838, all of the disclosuresof which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to polyaxial bone screws for use inbone surgery, particularly spinal surgery and particularly to suchscrews that have pressure inserts.

Bone screws are utilized in many types of spinal surgery in order tosecure various implants to vertebrae along the spinal column for thepurpose of stabilizing and/or adjusting spinal alignment. Although bothclosed-ended and open-ended bone screws are known, open-ended screws areparticularly well suited for connections to rods and connector arms,because such rods or arms do not need to be passed through a closedbore, but rather can be laid or urged into an open channel within areceiver or head of such a screw.

Typical open-ended bone screws include a threaded shank with a pair ofparallel projecting branches or arms which form a yoke with a U-shapedslot or channel to receive a rod. Hooks and other types of connectors,as are used in spinal fixation techniques, may also include open endsfor receiving rods or portions of other structure.

A common mechanism for providing vertebral support is to implant bonescrews into certain bones which then in turn support a longitudinalstructure such as a rod, or are supported by such a rod. Bone screws ofthis type may have a fixed head or receiver relative to a shank thereof.In the fixed bone screws, the rod receiver head cannot be moved relativeto the shank and the rod must be favorably positioned in order for it tobe placed within the receiver head. This is sometimes very difficult orimpossible to do. Therefore, polyaxial bone screws are commonlypreferred.

Open-ended polyaxial bone screws allow rotation of the head or receiverabout the shank until a desired rotational position of the head isachieved relative to the shank. Thereafter, a rod can be inserted intothe head or receiver and eventually the receiver is locked or fixed in aparticular position relative to the shank. During the rod implantationprocess it is desirable to utilize bone screws or other bone anchorsthat have components, or inserts that remain within the bone screw andfurther remain properly aligned during what is sometimes a very lengthy,difficult procedure.

SUMMARY OF THE INVENTION

A polyaxial bone screw assembly according to the invention includes ashank having an upper portion and a body for fixation to a bone; a heador receiver defining an open channel; a multi-part or piece retainer forpivotally holding the upper portion in the receiver; and at least onecompression insert spaced above and apart from the retainer structure.The shank upper portion is bottom or up-loadable into the receiver,cooperates with the retainer, and has a top end which extends above atop surface of the retainer, the retainer having polyaxial motion withrespect to the receiver, and the retainer including more than onediscrete piece, each piece frictionally engageable with the shank upperportion, slidably engageable with the receiver and located between theshank upper portion and the receiver and spaced below the insert. Thecompression insert includes arms defining a U-shaped channel forreceiving a longitudinal connecting member, the arms preferablyextending upwardly beyond a periphery of the connecting member beingreceived within the U-shaped channel. In some embodiments, thecompression insert arms directly engage a closure top to lock thepolyaxial mechanism of the screw while capturing but not necessarilylocking the longitudinal connecting member within the receiver. In otherembodiments, an alternative closure top directly engages a longitudinalconnecting member that in turn engages the lower pressure insert,pressing the insert into frictional engagement with the upper portion ofthe bone screw shank to lock the polyaxial mechanism and fix thelongitudinal connecting member with respect to the screw.

An alternative embodiment of a polyaxial screw according to theinvention includes an insert and closure top combination that providesfor some sagittal plane angulation of a longitudinal connecting memberbeing held by the screw. The insert and closure top each include convexor domed shaped surfaces facing the longitudinal connecting member. Thedomed surface of the closure top may be integral with or otherwiseattached to a remainder of the closure top.

Other alternative polyaxial and mono-axial bone screws according to theinvention include a deformable insert for closely engaging a connectingmember that may be hard or of a deformable or elastic material.

It is an object of the invention to provide apparatus and methods thatare easy to use and especially adapted for the intended use thereof andwherein the tools are comparatively inexpensive to produce.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged exploded perspective view of a polyaxial bonescrew assembly according to the present invention including a shank, areceiver, a retainer having two discreet pieces, a compression insertand a closure top.

FIG. 2 is an enlarged top plan view of the two-piece retainer of FIG. 1.

FIG. 3 is an enlarged cross-sectional view taken along the line 3-3 ofFIG. 2.

FIG. 4 is an enlarged and partial top plan view of the shank of FIG. 1.

FIG. 5 is an enlarged and partial front elevational view of the shank ofFIG. 1.

FIG. 6 is an enlarged and partial front elevational view of the shank,retainer pieces and receiver of FIG. 1 with portions broken away to showthe detail thereof and shown in an early stage of assembly.

FIG. 7 is an enlarged and partial front elevational view with portionsbroken away, similar to FIG. 6, shown in a later stage of assembly.

FIG. 8 is an enlarged and partial front elevational view of the shankretainer pieces, compression insert, receiver and closure top of FIG. 1,shown fully assembled (without a longitudinal connecting member), withportions broken away to show the detail thereof.

FIG. 9 is an enlarged and partial cross-sectional view taken along theline 9-9 of FIG. 8.

FIG. 10 is an enlarged front elevational view of an alternative closuretop for use with the assembly of FIG. 1.

FIG. 11 is an enlarged perspective view of the alternative closure topof FIG. 10.

FIG. 12 is an enlarged and partial side elevational view of the assemblyof FIG. 1 shown with the alternative closure top of FIG. 10 and alongitudinal connecting member.

FIG. 13 is an enlarged and partial cross-sectional view taken along theline 13-13 of FIG. 12.

FIG. 14 is an enlarged and partial cross-sectional view taken along theline 14-14 of FIG. 13.

FIG. 15 is an enlarged and partial exploded perspective view of asecond, alternative embodiment of a polyaxial bone screw assemblyaccording to the present invention including a shank, a receiver, aretainer having two discreet pieces, a compression insert, a pivotinsert, and a closure top, and further shown with a longitudinalconnecting member in the form of a rod.

FIG. 16 is an enlarged perspective view of the pivot insert of FIG. 15.

FIG. 17 is an enlarged top plan view of the pivot insert of FIG. 15.

FIG. 18 is an enlarged side elevational view of the pivot insert of FIG.15.

FIG. 19 is a cross-sectional view taken along the line 19-19 of FIG. 17.

FIG. 20 is an enlarged front elevational view of the pivot insert ofFIG. 15.

FIG. 21 is an enlarged bottom plan view of the pivot insert of FIG. 15.

FIG. 22 is an enlarged and partial front elevational view of theassembly of FIG. 15, with portions broken away to show the detailthereof, shown fully assembled without the longitudinal connectingmember.

FIG. 23 is an enlarged and partial cross-sectional view taken along theline 23-23 of FIG. 22.

FIG. 24 is an enlarged and partial front elevational view of theassembly of FIG. 15, with portions broken away to show the detailthereof and shown fully assembled with the longitudinal connectingmember.

FIG. 25 is an enlarged and partial cross-sectional view taken along theline 25-25 of FIG. 24 and showing a degree of angulation of thelongitudinal connecting member in phantom.

FIG. 26 is an enlarged front elevational view of an alternative closuretop for use with assemblies of the invention.

FIG. 27 is an enlarged cross-sectional view taken along the line 27-27of FIG. 26.

FIG. 28 is an enlarged and partial exploded perspective view of a third,alternative embodiment of a polyaxial bone screw assembly according tothe present invention including a shank, a receiver, a retainer havingtwo discreet pieces, a compression insert, a pivot insert, and a closuretop, and further shown with a longitudinal connecting member in the formof a rod.

FIG. 29 is an enlarged perspective view of the two piece retainer ofFIG. 28.

FIG. 30 is an enlarged front elevational view of the receiver of FIG.28.

FIG. 31 is an enlarged side elevational view of the receiver of FIG. 28with portions broken away to show the detail thereof.

FIG. 32 is an enlarged cross-sectional view taken along the line 32-32of FIG. 30.

FIG. 33 is an enlarged perspective view of the compression insert ofFIG. 28.

FIG. 34 is an enlarged top plan view of the compression insert of FIG.28.

FIG. 35 is an enlarged bottom plan view of the compression insert ofFIG. 28.

FIG. 36 is an enlarged top plan view of the pivot insert of FIG. 28.

FIG. 37 is an enlarged bottom plan view of the pivot insert of FIG. 36.

FIG. 38 is an enlarged side elevational view of the pivot insert of FIG.36.

FIG. 39 is an enlarged front elevational view of the pivot insert ofFIG. 36.

FIG. 40 is an enlarged cross-sectional view taken along the line 40-40of FIG. 36.

FIG. 41 is an enlarged perspective view of the pivot insert andcompression insert of FIG. 28.

FIG. 42 is an enlarged perspective view of the pivot insert andcompression insert of FIG. 41 shown assembled.

FIG. 43 is an enlarged and partial side elevational view of the assemblyof FIG. 28 shown fully assembled with the rod.

FIG. 44 is an enlarged and partial cross-sectional view taken along theline 44-44 of FIG. 43.

FIG. 45 is an enlarged and partial side elevational view of the assemblyof FIG. 43 with portions broken away to show the detail thereof andshown with zero degree rod toggle.

FIG. 46 is an enlarged and partial side elevational view of the assemblyof FIG. 43 with portions broken away to show the detail thereof andshown with three degree rod toggle.

FIG. 47 is an enlarged and partial side elevational view of the assemblyof FIG. 43 with portions broken away to show the detail thereof andshown with six degree rod toggle.

FIG. 48 is an enlarged and partial and partially exploded perspectiveview of the bone screw assembly of FIG. 28 shown with an alternativeclosure top.

FIG. 49 is an enlarged and partial side elevational view of the assemblyof FIG. 48.

FIG. 50 is an enlarged and partial cross-sectional view taken along theline 50-50 of FIG. 49.

FIG. 51 is an enlarged and partial, partially exploded perspective viewof a fourth, alternative embodiment of a polyaxial bone screw assemblyaccording to the present invention including a shank, a receiver, aretainer having two discreet pieces, a compression insert, a connectingmember support insert, and a closure top, and further shown with alongitudinal connecting member in the form of a deformable rod.

FIG. 52 is an enlarged exploded perspective view of the compressioninsert and support insert of FIG. 51.

FIG. 53 is an enlarged perspective view, similar to FIG. 52, showing thecompression insert and support insert assembled.

FIG. 54 is an enlarged top plan view of the connecting member supportinsert of FIG. 51.

FIG. 55 is an enlarged bottom plan view of the support insert of FIG.54.

FIG. 56 is an enlarged side elevational view of the support insert ofFIG. 54.

FIG. 57 is an enlarged front elevational view of the support insert ofFIG. 54.

FIG. 58 is an enlarged cross-sectional view taken along the line 58-58of FIG. 54.

FIG. 59 is a reduced side elevational view of the assembly of FIG. 51.

FIG. 60 is an enlarged and partial cross-sectional view taken along theline 60-60 of FIG. 59.

FIG. 61 is a reduced and partial cross-sectional view taken along theline 61-61 of FIG. 60.

FIG. 62 is an enlarged and partial side elevational view of the bonescrew assembly of FIG. 59 shown with a second bone screw of FIG. 59attached to the rod and an elastic spacer located between the two bonescrews.

FIG. 63 is an enlarged cross-sectional view taken along the line 63-63of FIG. 62.

FIG. 64 is an enlarged exploded side elevational view of a fifth,alternative embodiment of a mono-axial bone screw assembly according tothe present invention including a shank, a connecting member supportinsert, and a closure top, and further shown with a longitudinalconnecting member in the form of a deformable rod.

FIG. 65 is an enlarged top plan view of the support insert of FIG. 64.

FIG. 66 is an enlarged bottom plan view of the support insert of FIG.64.

FIG. 67 is an enlarged cross-sectional view taken along the line 67-67of FIG. 65.

FIG. 68 is an enlarged side elevational view, similar to FIG. 64,showing the bone screw assembly of FIG. 64 assembled.

FIG. 69 is an enlarged cross-sectional view taken along the line 69-69of FIG. 68.

FIG. 70 is an enlarged cross-sectional view taken along the line 70-70of FIG. 69.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the bone attachment structures in actual use.

With reference to FIGS. 1-14 the reference number 1 generally representsa polyaxial bone screw apparatus or assembly according to the presentinvention. The assembly 1 includes a shank 4, that further includes abody 6 integral with an upwardly extending upper portion or capturestructure 8; a receiver 10; a retainer structure, generally 12, havingtwo or more pieces; and a compression or pressure insert 14. The shank4, receiver 10, retainer structure 12 pieces and pressure insert 14preferably are assembled prior to implantation of the shank body 6 intoa vertebra (not shown).

FIG. 1 further shows a closure structure 18 of the invention forcapturing a longitudinal member such as a hard, inelastic rod 21 (shown,e.g., in FIG. 12) within the pressure insert 14 which in turn engages anupper curved area of the shank upper portion and biases the retainerstructure 12 pieces into fixed frictional contact with both the shankupper portion 8 and the receiver 10, so as to capture, and in someembodiments, fix the longitudinal connecting member 21 within thereceiver 10 and thus fix the member 21 relative to the vertebra. Theillustrated rod 21 is hard, non-elastic and cylindrical, having an outercylindrical surface 22. In other embodiments, the rod 21 may bedeformable and/or of a different cross-sectional geometry, as will bedescribed in greater detail below. The upper curved area of the shankupper portion 8 is spaced above the retainer 12 and the retainer 12 isdisposed between the shank upper portion 8 and the receiver 10. Thereceiver 10 and the shank 4 cooperate in such a manner that the receiver10 and the shank 4 can be secured at any of a plurality of angles,articulations or rotational alignments relative to one another andwithin a selected range of angles both from side to side and from frontto rear, to enable flexible or articulated engagement of the receiver 10with the shank 4 until both are locked or fixed relative to each othernear the end of an implantation procedure. In some embodiments, theshank upper portion 8 may further include a radially extending shelf,extension or resilient, compressible and/or split ring to aid in holdingthe retainer 12 pieces in a desired, fixed location with respect to theshank upper portion 8.

The shank 4, best illustrated in FIGS. 1-9, is elongate, with the shankbody 6 having a helically wound bone implantable thread 24 (single ordual lead thread form) extending from near a neck 26 located adjacent tothe upper portion or capture structure 8, to a tip 28 of the body 6 andextending radially outwardly therefrom. During use, the body 6 utilizingthe thread 24 for gripping and advancement is implanted into a vertebraleading with the tip 28 and driven down into the vertebra with aninstallation or driving tool (not shown), so as to be implanted in thevertebra to near the neck 26, as more fully described in the paragraphsbelow. The shank 4 has an elongate axis of rotation generally identifiedby the reference letter A.

The neck 26 extends axially upward from the shank body 6. The neck 26may be of slightly reduced radius as compared to an adjacent upper endor top 32 of the body 6 where the thread 24 terminates. Furtherextending axially and outwardly from the neck 26 is the shank upperportion 8 that provides a connective or capture apparatus disposed at adistance from the upper end 32 and thus at a distance from a vertebrawhen the body 6 is implanted in such vertebra.

The shank upper portion or capture structure 8 is configured forconnecting the shank 4 to the receiver 10 and capturing the shank upperportion structure in the receiver 10. In the embodiment shown, thestructure 8 has a substantially spherical body 38. An upper surface endportion 40 of the body 38 is adjacent to a planar annular top surface42. The top surface 42 is disposed perpendicular to the axis A. It isforeseen that in other embodiments of the invention, the spherical body38 may alternatively take the form of a polyhedral formation or othercurved shape, such as, for example, cylindrical or conical. The uppersurface portion 40 is substantially spherical and terminates at thenarrow top annular surface 42. The portion 40 forms a partial dome nearthe surface 42 for closely engaging a spherical surface of the insert 14as will be described in greater detail below. A lower surface portion 44of the spherical body 38 extends from the upper surface portion 40 tothe shank neck 26. The lower surface portion 44 and an adjacent portion45 of the neck 26 closely engage inner surfaces of the retainer 12pieces as will be described in greater detail below.

The shank 4 further includes a tool engagement structure or inner drive52 formed in the top surface 42. The illustrated drive 52 is a hex driveor aperture for engaging a similarly shaped driving tool (not shown) forboth driving and rotating the shank body 6 into a vertebra. Other shapeddrives and cooperating tools are possible, such as grooved,multi-lobular, etc. While not required in accordance with the practiceof the invention, the lower surface portion 44 and/or the upper surface40 may be scored, threaded, ridged or knurled to further increasefrictional engagement between such surfaces and respective cooperatingsurfaces of the retainer 12 and the insert 14.

The shank 4 shown in the drawings is cannulated, having a small centralbore 54 extending an entire length of the shank 4 along the axis A fromthe internal drive 52 to the tip 28. The bore 54 is coaxial with thethreaded body 6. The bore 54 provides a passage through the shank 4interior for a length of wire (not shown) inserted into a vertebra priorto the insertion of the shank body 6, the wire providing a guide forinsertion of the shank body 6 into the vertebra 15.

To provide a biologically active interface with the bone, the threadedshank body 6 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or ongrowth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

With particular reference to FIGS. 1 and 6-9, the receiver 10 has agenerally U-shaped appearance with a discontinuous partially cylindricaland partially spherical inner profile and a partially curved andpartially faceted outer profile. The receiver 10 has an axis of rotationB that is shown in FIG. 1 as being aligned with and the same as the axisof rotation A of the shank 4, such orientation being desirable duringassembly of the receiver 10 with the shank 4, the retainer pieces 12 andthe insert 14. After the receiver 10 is pivotally attached to the shank4, and the assembly 1 is implanted in a vertebra (not shown), the axis Bis typically disposed at an angle with respect to the axis A.

The receiver 10 includes a base 60 integral with a pair of opposedupstanding arms 62 forming a cradle and defining a U-shaped channel 64between the arms 62 with an upper opening, generally 66, and a lowerseat 68, the channel 64 having a width for operably snugly receiving therod 21 between the arms 62. Each of the arms 62 has an interior surface70 that defines the inner cylindrical profile and includes a partialhelically wound guide and advancement structure 72. In the illustratedembodiment, the guide and advancement structure 72 is a partialhelically wound interlocking flange form configured to mate underrotation with a similar structure on the closure structure 18, asdescribed more fully below. However, it is foreseen that the guide andadvancement structure 72 could alternatively be a square-shaped thread,a buttress thread, a reverse angle thread or other thread-like ornon-thread-like helically wound discontinuous advancement structure foroperably guiding under rotation and advancing the closure structure 18downward between the arms 62, as well as eventual torquing when theclosure structure 18 abuts against the rod 21 in some embodiments orabuts against the compression insert 14 in other embodiments.

An opposed pair of tool receiving and engaging apertures 74 are formedon outer surfaces 76 of the arms 62. As illustrated, the apertures 74 donot extend completely through the arms 62. At each aperture 74, a thinwall 78 partially defines the aperture and may be crimped or pushedinwardly toward and into a cooperating aperture of the pressure insert14 as will be described in greater detail below. Alternatively, thereceiver 10 or the pressure insert 14 may be equipped with spring tabsthat bias against a respective pressure insert or receiver to prohibitrotational movement of the insert 14 about the receiver axis B once theinsert 14 is loaded in the receiver 10 and positioned with therod-receiving channel of the insert 14 in alignment with the U-shapedchannel 64 of the receiver.

Communicating with the U-shaped channel 64 of the receiver 10 is achamber or cavity 90 defined in part by a substantially cylindricalupper portion 92, a substantially conical middle portion 93 and by alower inner substantially spherical retainer seating surface 94 of thebase 60. The upper portion 92 is located below the guide and advancementstructures 72 and may include one or more cylindrical surfaces forsliding cooperation with an insert or inserts. The walls 78 defining theapertures 74 communicate with the cylindrical upper portion 92. Thesubstantially conical mid-portion 93 is adjacent to the upper portion 92near the seating surface 68 of the U-shaped channel 64. The mid-portion93 is also adjacent to the seating surface 94. The seating surface 94 issized and shaped for slidable mating and eventual frictional engagementwith the retainer pieces 12, as described more fully below. The cavity90 opens into the U-shaped channel 64 and also to a lower neck 96defining a bore or circular opening that communicates with a lowerexterior 98 of the base 60. The circular neck 96 is coaxially alignedwith the rotational axis B of the receiver 10. The neck 96 is sized andshaped to be smaller than an outer radial dimension of the operationallyassembled retainer pieces 12, as will be discussed further below, so asto form a restriction at the location of the neck relative to theretainer 12, to prevent the retainer 12 from passing from the cavity 90and out to the lower exterior 98 of the receiver 10 when the retainer 12is seated and assembled about the shank upper portion 8.

With particular reference to FIGS. 1-3 and 6-7, the two-part retainer 12is used to retain the upper portion or capture structure 8 of the shank4 within the receiver 10 and also articulate the shank body 6 withrespect to the receiver 10. The retainer pieces are each sized andshaped to frictionally engage the shank upper portion while beingpivotally mounted with respect to the receiver 10, the pieces locatedbelow the upper surface portion 40 and between the lower surface portion44 and the receiver base 60 and being articulatable with respect to thereceiver seating surface 94 until the shank 6 is fixed in a desiredposition with respect to the receiver base 60. The retainer structure12, best illustrated in FIGS. 1-3, has an operational central axis Cthat is the same as the axis A associated with the shank 4. Thestructure 12 includes a first piece or part 101 and an opposinglypositioned, and in this embodiment a substantially identical or mirrorimage second piece or part 102. The parts 101 and 102 provide a collarabout the shank upper portion 8 and a portion of the shank neck 26, withthe upper surface portion 40 extending upwardly above the parts 101 and102 and towards the opening 66 within the receiver 10, and each of theparts 101 and 102 disposed between the portion 8 and the receiver 10when installed, as will be discussed more fully below. Once installedand locked into position, the parts or pieces 101 and 102 closely gripboth the shank 4 at the surfaces 44 and 45 and also the receiver seatingsurface 94, providing an even and uniform gripping surface between theshank 4 and the receiver 10 at the spherical seating surface 94 whenforce is directed onto the shank domed surface 40 by the insert 14cooperating with the rod 21 and/or the closure structure 18, or by othertypes of longitudinal members, inserts and closure structures.

Although a two-piece retainer structure 12 is illustrated herein, it isforeseen that the retainer structure may be made up of more than twopieces, each frictionally matable with both the shank upper portion orcapture structure 8 and the seating surface 94 of the receiver 10. Thepieces may also be of varying sizes and not necessarily mirror images ofone another. The mating surfaces of the shank upper portion andcooperating retainer pieces may further include planar surfaces that maybe tapered or parallel or other curved surfaces, for example,cylindrical or conical in form. Additionally, it is foreseen that thepieces may include a plurality of planar or curved surfaces, such asundulating or zig-zag surfaces, forming peaks and valleys that wouldcooperate and mate with similarly configured surfaces on the shank upperportion. Furthermore, the parts 101 and 102 may be in frictional contactor spaced from one another when fully installed in the receiver 10 andin contact with the shank upper portion 8. The parts 101 and 102 canalso be interlocking with each other or in some other way cooperatingwith each other and/or with the compression insert in the receivercavity such that the shank may be uploaded into the receiver in a“snap-on” or “pop-on” fashion allowing the receiver and pre-loadedretainer pieces and compression insert to be assembled with the shankeither at the factory, by surgical staff before implantation of theassembly 1, or after the shank alone is implanted into a vertebra.

Each retainer part 101 and 102 includes a substantially spherical outersurface, 104 and 105, respectively, each having a radius substantiallysimilar to a radius of the receiver seating surface 94. The parts 101and 102 further include respective planar top surfaces 107 and 108 andrespective planar bottom surfaces 110 and 111. The illustrated surface107 and the surface 110 are substantially parallel. The illustratedsurface 108 and the surface 111 are substantially parallel. Adjacent tothe top surfaces 107 and 108 are respective substantially sphericalinner surfaces 114 and 115. The surface 114 is adjacent to an innerfrusto-conical surface 118 and the surface 115 is adjacent to an innerfrusto-conical surface 119. The inner spherical surfaces 114 and 115each have a radius identical or substantially similar to the radius ofthe shank upper portion body 38, being sized and shaped to closelyfrictionally mate with the lower surface 44 of the body 38. Thefrusto-conical surfaces 118 and 119 are sized and shaped to be closely,frictionally received about the shank neck 26 at the surface 45. Asillustrated in FIG. 9, for example, the inner surfaces 114 and 115 andthe outer spherical surfaces 104 and 105 are advantageously sized toallow for clearance between the retainer 12 and the insert 14 whenpivoting the shank 4 with respect to the receiver 10 into a desiredposition. With particular reference to FIGS. 8-9, when the retainerstructure parts 101 and 102 are operationally disposed in the receiver10, the inner surfaces 118 and 119 are seated on the shank neck surface45 and frictionally engaged thereto and the inner spherical surfaces 114and 115 are frictionally gripping the shank body 38 at the surface 44,while the outer spherical surfaces 104 and 105 are free to slide withrespect to the receiver seating surface 94 until locked into place bypressure from the closure 18 pressing on the insert 14 that in turnpresses exclusively on the shank domed upper surface 40.

With particular reference to FIGS. 2 and 8, the retainer part or piece101 further includes opposed end walls 132 and 133, extending from theouter surface 104 to the inner walls 114 and 118. The end walls 132 and133 are disposed at an oblique angle to the respective top and bottomsurfaces 107 and 110. The retainer part 102 further includes end walls134 and 135, extending from the outer surface 105 to the inner walls 115and 119. The end walls 134 and 135 are disposed at an oblique angle tothe respective top and bottom surfaces 108 and 111. In some embodimentsaccording to the invention, each of the walls 132, 133, 134 and 135 areoriented substantially perpendicular to the top and bottom surfaces ofthe respective retainer pieces. Angles other than what is illustratedmay also be used. Each of the walls 132, 133, 134 and 135 may includebeveled surfaces. The retainer parts 101 and 102 are configured suchthat, when operationally disposed in the receiver 10, with thesubstantially spherical surfaces 104 and 105 in sliding frictionalcontact with the spherical seating surface 94, and with the innersurfaces 118 and 119 seated on the frusto-conical neck surface 45 of theshank 4, the end walls 132 and 133 are closely spaced or in contact withthe respective end walls 134 and 135, as illustrated in FIGS. 2, 3 and8. It is foreseen that also in accordance with the invention, to provideadditional clearance during installation, the illustrated parts 101 and102 are configured such that the end walls 132 and 133 are in spaced,substantially parallel relation with the respective end walls 134 and135, when fully installed in the bone screw receiver 10.

With particular reference to FIGS. 1 and 8-9, the illustratedcompression insert 14 is sized and shaped to be received by anddownloaded into the receiver 10 at the upper opening 66. However, inother embodiments of the invention, the insert 14 may be sized foruploading or downloading into the receiver 10. The compression insert 14has an operational central axis that is the same as the central axis Bof the receiver 10. The compression insert 14 has a central channel orthrough bore substantially defined by an inner cylindrical surface 141coaxial with an inner partially spherical surface 142. The compressioninsert 14 through bore is sized and shaped to receive a driving tool(not shown) therethrough that engages the shank drive feature 52 whenthe shank body 6 is driven into bone. The surface 142 is sized andshaped to slidingly receive and ultimately frictionally engage thesubstantially spherical or domed surface 40 of the shank upper portion 8such that the surface 142 initially slidingly and pivotally mates withthe spherical surface 40. The surface 142 may include a roughening orsurface finish to aid in frictional contact between the surface 142 andthe surface 40, once a desired angle of articulation of the shank 4 withrespect to the receiver 10 is reached.

The compression insert 14 also includes a pair of arms 144, each havinga top surface 145, with a pair of U-shaped saddle-like surfaces 146running between the arms and forming a seat for a longitudinalconnecting member, such as the rod 21. A centrally located lower planarsurface 147 is disposed between portions of the saddle-like surfaces146, the planar surface 147 partially defining an opening of the centralchannel at the cylindrical surface 141. The planar surface 147 isdisposed substantially perpendicular to the cylindrical surface 141.Portions of the saddle surfaces 146 also communicate with the boredefined by the cylindrical surface 141. The curved surfaces 146 aresized and shaped to closely receive the cylindrical rod 21 or otherlongitudinal connecting member. The saddle-like surfaces 146 extendbetween substantially planar opposed inner surfaces 148 of the arms 144,the inner surfaces 148 extending to the top surfaces 145 of the arms.The spaced saddle-like surfaces 146 form a lower seat 150 located near alower or bottom surface 152 of the insert 14. The surface 152 slopesupwardly from and communicates with the inner spherical surface 142, thesurface 152 allowing for clearance between the insert 14 and theretainer pieces 12 as best shown in FIG. 8. The arms 144 have a heightdimension such that the top surfaces 145 are disposed above the rod 21or other longitudinal connecting member captured by the assembly 1. Thearms 144 preferably have an adequate thickness so that the arms 144closely capture the rod 21 therebetween and also are supported by thecylindrical wall 92 defining the receiver cavity 90 directly under theguide and advancement structure 72.

In operation, the lower seat 150 (as well as at least a substantialportion of a remainder of the saddle 146) frictionally engages an outersurface 22 of the rod 21. A frusto-conical base outer surface 154extends generally from the arms 144 to the bottom surface 152. Theillustrated insert 14 is partially cylindrical and partially conicalwith the surface 154 sloping upwardly to outer surfaces 155 of the arms144. Formed in the surfaces 155 and located centrally with respect toeach arm 144 is a shallow groove or depression 156. Each illustratedgroove 156 is substantially U-shaped and is sized and shaped tocooperate with the apertures 74 and receiver thin inner walls 78 as willbe described in greater detail below. The grooves 156 may be of anyshape and are preferably elongate, running parallel to a central axis ofthe insert 14 that is operationally coaxial with the axis B of thereceiver 10. In some embodiments of the invention, the grooves ordepressions 156 may be substantially flat surfaces formed by planing thecylindrical surface 155. The compression or pressure insert 14ultimately seats on the shank upper portion 8 and is disposedsubstantially in the upper cylindrical portion 92 of the cavity 90, withthe walls 78 being pressed or crimped into each depression 156 to holdthe insert 14 in a desired alignment with respect to the rod 21 as willbe described in greater detail below. In operation, the insert 14extends at least partially in the channel 64 of the receiver 10 suchthat the saddle 146 surface substantially contacts and engages the outersurface 22 of the rod 21 when such rod is placed in the receiver 10 andthe closure structure or top 18 is tightened thereon.

With reference to FIGS. 12, 13 and 14, the illustrated elongate rod orlongitudinal connecting member 21 can be any of a variety of implantsutilized in reconstructive spinal surgery, but is typically acylindrical, elongate structure having the outer substantially smooth,cylindrical surface 22 of uniform diameter. The rod 21 may be made froma variety of metals, metal alloys and deformable and less compressibleplastics, including, but not limited to rods made of elastomeric,polyetheretherketone (PEEK) and other types of materials.

Longitudinal connecting members for use with the assembly 1 may take avariety of shapes, including but not limited to rods or bars of oval,rectangular or other curved or polygonal cross-section. The shape of theinsert 14 channel or saddle 146 may be modified so as to closely hold,and if desired, fix the longitudinal connecting member to the assembly1. Some embodiments of the assembly 1 may also be used with a tensionedcord. Such a cord may be made from a variety of materials, includingpolyester or other plastic fibers, strands or threads, such aspolyethylene-terephthalate. Furthermore, the longitudinal connector maybe a component of a longer overall dynamic stabilization connectingmember, with cylindrical or bar-shaped portions sized and shaped forbeing received by the compression insert 14 of the receiver having au-shaped channel (or rectangular- or other-shaped channel) for closelyreceiving the longitudinal connecting member. The longitudinalconnecting member may be integral or otherwise fixed to a bendable ordamping component that is sized and shaped to be located betweenadjacent pairs of bone screw assemblies 1, for example. A dampingcomponent or bumper may be attached to the longitudinal connectingmember at one or both sides of the bone screw assembly 1. A rod or bar(or rod or bar component) of a longitudinal connecting member may bemade of a variety of materials ranging from deformable plastics to hardmetals, depending upon the desired application. Thus, bars and rods ofthe invention may be made of materials including, but not limited tometal and metal alloys including but not limited to stainless steel,titanium, titanium alloys and cobalt chrome; or other suitablematerials, including plastic polymers such as polyetheretherketone(PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanesand composites, including composites containing carbon fiber, natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers.

With reference to FIGS. 1, 8 and 9, the first closure structure orclosure top 18 shown with the assembly 1 is rotatably received betweenthe spaced arms 62. It is noted that the closure 18 can be any of avariety of different types of closure structures for use in conjunctionwith the present invention with suitable mating structure on theupstanding arms 62. It is also foreseen that the closure top could be atwist-in or slide-in closure structure. The illustrated closurestructure 18 is substantially cylindrical and includes an outerhelically wound guide and advancement structure 162 in the form of aflange form that operably joins with the guide and advancement structure72 disposed on the arms 62 of the receiver 10. The flange form utilizedin accordance with the present invention may take a variety of forms,including those described in Applicant's U.S. Pat. No. 6,726,689, whichis incorporated herein by reference. It is also foreseen that accordingto the invention the closure structure guide and advancement structurecould alternatively be a buttress thread, a square thread, a reverseangle thread or other thread like or non-thread like helically woundadvancement structure for operably guiding under rotation and advancingthe closure structure 18 downward between the arms 62 and having such anature as to resist splaying of the arms 62 when the closure structure18 is advanced into the U-shaped channel 64. The illustrated closurestructure 18 also includes a top surface 164 with an internal drive 166in the form of an aperture that is illustrated as a star-shaped internaldrive such as that sold under the trademark TORX, or may be, forexample, a hex drive, or other internal drives such as slotted,tri-wing, spanner, two or more apertures of various shapes, and thelike. A driving tool (not shown) sized and shaped for engagement withthe internal drive 166 is used for both rotatable engagement and, ifneeded, disengagement of the closure 18 from the receiver arms 62. It isalso foreseen that the closure structure 18 may alternatively include abreak-off head designed to allow such a head to break from a base of theclosure at a preselected torque, for example, 70 to 140 inch pounds.Such a closure structure would also include a base having an internaldrive to be used for closure removal. A base or bottom surface 168 ofthe closure is illustrated as planar, but may include a point, points, arim or roughening for engagement with the surface 22 of the rod 21 incertain embodiments of the invention. The closure top 18 may furtherinclude a cannulation through bore (not shown) extending along a centralaxis thereof and through the top and bottom surfaces thereof. Such athrough bore provides a passage through the closure 18 interior for alength of wire (not shown) inserted therein to provide a guide forinsertion of the closure top into the receiver arms 62.

With particular reference to FIGS. 8 and 9, the closure top 18 is shownfully assembled with the receiver 10 and the insert 14, but without therod 21 or any other longitudinal connecting member. The closure top 18includes an annular base rim or step 170 adjacent the bottom surface168. The closure structure 18 is sized and shaped such that the annularrim 170 engages the top surfaces 145 of the insert 14 and presses theinsert 14 down into pressing engagement with the shank upper portion 8to lock the shank 4 in place with respect to the receiver 10. Thus, insome embodiments of the invention, the assembly 1 cooperates with a rod,cord, cable or other longitudinal connecting member to capture suchconnecting member within the receiver 10, but to allow the connectorsome freedom of movement within the receiver 10. In such applications,elastic spacers can be positioned around the connecting member andbetween the receivers. The closure 18 and insert 14 combination may alsobe desirable when the connecting member is made from a deformableplastic. In such embodiments, the closure bottom surface 168 may engageand frictionally hold the connecting member in place, but the polyaxialmechanism is firmly locked in place by the closure 18 directly engagingand pressing upon the insert 14 that in turn presses on the shank upperportion, desirably holding, but not over-stressing the longitudinalconnecting member at the cite of engagement with the bone screw. Also,if a longitudinal connecting member would eventually become partially ortotally disengaged from the closure bottom surface 168, for example, ifa plastic connecting member exhibits creep, the shank 4 wouldadvantageously remain fixed in position with respect to the receiverregardless of any movement of the connecting member within the receiver.

With reference to FIGS. 10-14 the assembly 1 of FIG. 1 is shown with therod 22 and a modified closure top 18′. Thus, the assembly shown in FIGS.12-14 is identified herein as the assembly 1′. The top 18′ includes aguide and advancement structure 162′, a top 164′ and an internal drive166′ identical or substantially similar in form and function to therespective guide and advancement structure 162, top 164, and internaldrive 166 of the closure top 18 previously described herein.Furthermore, the closure top 18′ includes a point 167′ and rim 168′bottom or base feature as compared to the planar bottom 168 of theclosure top 18. Similar to the closure top 18, the top 18′ includes anannular step or rim 170′ that in some embodiments may frictionallyengage the insert 14 similar to the step or rim 170 of the closure top18. However, in the embodiment shown in FIGS. 12-14, the point 167′ andthe rim 168′ frictionally engage the rod 21, while the step 170′ remainsspaced from top surfaces 145 of the insert 14. The pressure of theclosure top 18′ bearing down on the rod 21 in turn presses the rodagainst the insert 14 thereby pressing the insert 14 into engagementwith the bone screw shank upper portion 8. Specifically, the rod 21 iscradled by and directly or abuttingly engages the insert 14 at thesaddle 146, as shown in FIGS. 13 and 14 and is biased against the saddle146 by pressure from the closure structure 18′, consequently biasing theinsert surface 142 against the shank upper portion 8 spherical surfaceportion 40, pressing the shank 4 downwardly in a direction toward thebase 60 of the receiver 10 when the assembly 1 is fully assembled,ultimately pressing the retainer pieces 101 and 102 into frictionalengagement with the receiver seating surface 94, thereby locking thepolyaxial mechanism of the bone screw assembly 1′. The shank 4 andretainer structure pieces 12 are thereby locked or held in positionrelative to the receiver 10 by the rod 21 firmly pushing downward on theinsert 14 that in turn pushes down on the shank upper surface 40.

Prior to the polyaxial bone screw assembly 1 or 1′ being placed in useaccording to the invention, the retainer structure pieces 101 and 102are typically first inserted or top-loaded into the receiver U-shapedchannel 64 at the opening 66, as shown in FIG. 6, and then into thecavity 90 to ultimately dispose the structure pieces 12 adjacent to theinner surface 94 of the receiver 10. Alternatively, one of the retainerstructure pieces 101 may be inserted or top-loaded into the channel 64at the opening 66, while the other retainer structure piece 102, mayinserted or bottom-loaded into the cavity 90 at the lower neck 96.Alternatively, both pieces 101 and 102 may be uploaded at the neck 96.

With reference to FIG. 7, after the retainer pieces 101 and 102 aredisposed in the cavity 90, the shank 4 is inserted or up-loaded into thereceiver 10 at the neck 96. The spherical body 38 of the shank upperportion 8 comes into contact with the inner surfaces 114 and 115 of therespective retainer pieces 101 and 102. Initially all three components,the shank upper portion 8, and the pieces 101 and 102 may move upwardlyinto the cavity 90. As the shank upper portion 8 continues to moveupwardly and into the cavity 90, the retainer structure pieces 101 and102 pivot about edges thereof and then begin to move downwardly towardthe base 60 until in operational alignment as shown, for example, inFIGS. 8, 9, 13 and 14, with the inner frusto-conical surfaces 118 and119 abutting and seated upon the surface 45 of the shank neck 26. At thesame time, the inner spherical surfaces 114 and 116 frictionally engagethe lower spherical surface portion 44 of the shank upper portion 8.Subsequent slight downward movement (directed away from the top opening66) by the shank 4, as well as the frictionally engaged retainer pieces101 and 102, seats the shank/retainer structure assembly in the receivercavity 90, with the retainer outer spherical surfaces 104 and 105 insliding engagement with the receiver seating surface 94. The retainerstructure pieces 12, now fully seated in the receiver 10 are coaxiallyaligned with the shank upper portion. At this time, the shank upperportion 8, the retainer structure 12, the receiver seating surface 94and the lower aperture or neck 96 cooperate to maintain the shank body 6in pivotal and rotational relation with the receiver 10. Only theretainer structure 12 is in slidable engagement with the receiverspherical seating surface 94. Both the shank upper portion 8 and thethreaded portion of the shank body 6 are in spaced relation with thereceiver 10. At this point there is no substantial outward or downwardpressure on the shank upper portion 8 so the retainer 12 easily rotateswith the shank 6 within the receiver chamber, such rotation being of aball and socket type with the angle of rotation restricted only byengagement of the shank neck 26 with the neck 96 of the receiver 10. Aspring-ring located between the upper portion 8 and retainer 12 canprovide frictional engagement between the parts to stabilize andminimize unwanted movement with respect to the shank during rodinsertion.

Then, the insert 14 is inserted into the receiver channel 64 at theopening 66 with the arms 144 aligned in the channel 64 between the guideand advancement structures 72. The insert 14 is then moved downwardly inthe channel and toward the cavity 90. Once the arms 144 are locatedgenerally below the guide and advancement structure 72, the insert 14 isrotated about the axis B of the receiver 10. The arms 144 fit within thecylindrical walls 92. Once the arms 144 are located directly below theguide and advancement structures 72, rotation is ceased and a tool (notshown) is used to press the thin walls 78 of the receiver 10 into therecesses 156 of the insert 14. The insert 14 is now locked into placeinside the receiver 10 with the guide and advancement structures 72prohibiting upward movement of the insert 14 out of the channel 64. Asillustrated in FIGS. 8, 9, 14 and 15, the insert 14 seats on the shankupper portion surface 40 with the surface 142 in sliding engagement withthe surface 40. A run-out or relief area of the surface 92 locateddirectly beneath the receiver guide and advancement structure 72 issized and shaped to allow for some upward and downward movement of theinsert 14 toward and away from the shank upper portion 8 such that theshank 4 is freely pivotable with respect to the receiver 10 until theinsert 14 is pressed down upon the upper portion 8, placing the shankupper portion 8 into locking frictional engagement with the receiver 10at the surface 94. With respect to the assembly 1, the shank is lockedinto place by pressure from the closure structure 18 onto the insert 14,while in the assembly 1′, the closure structure 18′ presses on the rod21 that in turn presses on the insert 14 that in turn presses down uponthe shank upper portion 8.

The bone screw assembly made up of the assembled shank 4, receiver 10,retainer pieces 12 and insert 14 is then normally screwed into a bone,such as vertebra, by rotation of the shank 4 using a suitable drivingtool (not shown) that operably drives and rotates the shank body 6 byengagement thereof at the internal drive 52. Specifically, the vertebra(not shown) may be pre-drilled to minimize stressing the bone and have aguide wire (not shown) inserted to provide a guide for the placement andangle of the shank 4 with respect to the vertebra. A further tap holemay be made using a tap with the guide wire as a guide. Then, the bonescrew assembly is threaded onto the guide wire utilizing the cannulationbore 54 by first threading the wire into the opening at the bottom 28and then out of the top opening at the drive feature 52. The shank 4 isthen driven into the vertebra using the wire as a placement guide. It isforeseen that the bone screw assemblies 1, 1′, the rod 21 (also having acentral lumen in some embodiments) and the closure top 18 or 18′ (alsowith a central bore) can be inserted in a percutaneous or minimallyinvasive surgical manner, utilizing guide wires.

With reference to FIGS. 13 and 14, for example, of the assembly 1′, therod 21 is eventually positioned in an open or percutaneous manner incooperation with the at least two bone screw assemblies 1′. Alignment ofthe rod surface 22 with the saddle 146 of the insert 14 is initiallyprovided and then maintained by the crimped walls 78 of the receiver 10.The closure structure 18′ is then inserted into and advanced between thearms 62 of each of the receivers 10. The closure structure 18′ isrotated, using a tool engaged with the inner drive 166′ until a selectedpressure is reached at which point the rod 21 engages the saddle 146 andthe rod is urged toward, but not in contact with the lower seat of thereceiver 10 that defines the U-shaped channel 64. For example, about 80to about 120 inch pounds pressure may be required for fixing the bonescrew shank 6 with respect to the receiver 10.

As the closure structure 18′ rotates and moves downwardly into therespective receiver 10, the point 167′ and rim 168′ engage and penetratethe rod surface 22, the closure structure 18′ pressing against andbiasing the rod 21 into engagement with the compression insert 14 thatoperably produces a frictional engagement between the insert surface 142and the shank surface 40 and also urges the shank upper portion 8 towardthe retainer 12 and, in turn, the structure 12 in a direction toward thebase 60 of the receiver 10, so as to frictionally seat the sphericalsurfaces 104 and 105 against the internal spherical seating surface 94of the receiver 10, also fixing the shank 4 and the retainer 12 in aselected, rigid position relative to the receiver 10. At this time it isalso possible for the retainer 12 to expand somewhat for an even tighterfit in the receiver cavity lower seat 94.

If removal of the rod 21 from any of the bone screw assemblies 1 or 1′is necessary, or if it is desired to release the rod 21 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 166 or 166′ on the closurestructure 18 or 18′ to rotate and remove such closure structure from thecooperating receiver 10. Disassembly is then accomplished in reverseorder to the procedure described previously herein for assembly.

With reference to FIGS. 15-25, a second embodiment of a polyaxial bonescrew according to the invention, generally 201, includes a shank 204having a body 206 and an upper portion 208, a receiver 210, a two-pieceretainer 212, a compression insert 214, a pivot insert 216 and a closurestructure 218 and is shown with a longitudinal connecting member in theform of a hard, inelastic, substantially non-deformable rod 221 having asubstantially cylindrical outer surface 222. It is noted that theillustrated inserts and cooperating features of bone screws according tothe invention may also be used with one-piece retainers or rings.

The shank 204 is identical or substantially similar in form and functionto the shank 4 previously described herein with respect to the assembly1. Thus, the shank 204 includes a thread 224, a neck 226, a tip 228, aspherical body 238 with an upper surface portion 240, a planar annulartop 242, a lower surface portion/seating surface 244, a shank neckportion 245, and an internal drive 252 that are the same or similar inform and function to the respective thread 24, neck 26, tip 28,spherical body 38 with upper surface portion 40, planar annular top 42,lower surface portion/seating surface 244, shank neck portion 245, andinternal drive 252 of the shank 4 of the assembly 1.

The receiver 210 is identical or substantially similar in form andfunction to the receiver 10 previously described herein with respect tothe assembly 1. Thus, the receiver 210 includes a receiver base 260, apair of upstanding arms 262, a U-shaped channel 264, guide andadvancement structures 272, apertures 274, outer arm surfaces 276, innerwalls 278, a cavity or chamber 290, upper inner cylindrical walls 292,spherical seating surface 294, a neck 296 and a lower exterior 298 thatare the same or similar in form and function to the respective receiverbase 60, pair of upstanding arms 62, U-shaped channel 64, guide andadvancement structures 72, apertures 74, outer arm surfaces 76, innerwalls 78, cavity or camber 90, upper inner cylindrical walls 92,spherical seating surface 94, neck 96 and a lower exterior 98 of thereceiver 10 of the assembly 1.

The two piece retainer 212 is identical or substantially similar in formand function to the two-piece retainer 12 previously described hereinwith respect to the assembly 1. Thus, the retainer 212 includes a firstpiece 301 and a second piece 302 having respective outer sphericalsurfaces 304 and 305, respective top surfaces 307 and 308, respectiveinner spherical surfaces 314 and 315, respective inner frusto-conicalsurfaces 318 and 319 that are the same or similar in form and functionas the respective first piece 101, second piece 102, respective outerspherical surfaces 104 and 105, respective top surfaces 107 and 108,respective inner spherical surfaces 114 and 115 and respectivefrusto-conical surfaces 118 and 119 of the retainer 12 of the assembly1, as well as all other features thereof.

The compression insert 214 is substantially similar in form and functionto the insert 14 previously described herein with respect to theassembly 1. Thus, the insert 214 includes a cylindrical inner surface341, an inner spherical surface 342, a pair of spaced opposed arms 344having top surfaces 345, a pair of saddle shaped surfaces 346, a lowerplanar surface 347, inner planar arm surfaces 348, a saddle lower seat350, a bottom surface 352, a base outer surface 354, outer arm surfaces355, each having a groove or depression 356 that are the same or similarin form and function to the respective cylindrical inner surface 141,inner spherical surface 142, pair of spaced opposed arms 144 having topsurfaces 145, pair of saddle shaped surfaces 146, lower planar surface147, inner planar arm surfaces 148, saddle lower seat 150, bottomsurface 152, base outer surface 154, and outer arm surfaces 155, eachhaving a groove or depression 156 previously described herein withrespect to the assembly 1. Unlike the assembly 1, the compression insert214 of the assembly 201 further engages the pivot insert 216 at theplanar surface 345, with the cylindrical surface 341 receiving a portionof the pivot insert 216 as will be discussed in greater detail below.

The closure top 218 is substantially similar in form and function to thetop 18 previously described herein with respect to the assembly 1 withthe exception of a bottom surface thereof. Thus, the closure top 218includes a guide and advancement structure 362, a top surface 364, aninternal drive 366 and a bottom rim 370 that is identical orsubstantially similar in form and function to the respective guide andadvancement structure 162, the top surface 164, the internal drive 166and the bottom annular planar rim surface 170 of the closure top 18previously described herein with respect to the assembly 1. As shown,for example, in FIGS. 22 and 23, the closure top 218 is sized and shapedso that the bottom rim 370 directly frictionally engages the top surface345 of the compression insert 214, pushing the insert 214 in a directiontoward the receiver base 260 so that the insert 214 directlyfrictionally engages the shank upper portion 208 at the sphericalsurface 240 pushing the shank 204 downwardly and thus pressing theretainer pieces 212 into frictional engagement with the receiverspherical seat 294. Therefore, locking of the polyaxial mechanism is notsolely dependent upon the closure top 218 pressing on the rod 221 thatin turn presses the compression insert 214 into engagement with theshank 204.

Also, the closure top 218, rather than having a planar bottom surfacesuch as the bottom surface 168 of the closure top 18, has asubstantially domed or spherical bottom surface 368. As will bedescribed in greater detail below, the spherical surface 368 of theclosure top 218 cooperates with a curved surface of the pivot insert 216allowing for operative angulation or pivoting movement of thelongitudinal connecting member disposed therebetween in the sagittalplane.

With particular reference to FIGS. 16-21, the illustrated pivot insert216 is sized and shaped to be received by and downloaded into thereceiver 10 at the upper opening 66, followed by insertion into thepreviously inserted compression insert 214. The pivot insert 216 has anoperational central axis that is the same as the central axis of thereceiver 210 and the compression insert 214. A concave, substantiallyspherical bottom surface 379 of the insert 216 has a radius that issubstantially the same or only slightly larger than the radius of thespherical body 238 of the upper portion 208 of the shank 204, thesurface 379 being sized and shaped to slidingly receive the uppersurface portion 240 of the spherical body 238 when the pivot insert isseated within the compression insert 214. The concave surface 379partially defines an otherwise substantially cylindrical base 380 of thepivot insert 216, the base 380 having a substantially planar annularbottom rim surface 381 disposed about the spherical surface 379. Thebase 380 is sized and shaped to be received within the inner cylindricalsurface 341 of the compression insert 214. The base 380 is integral witha substantially ellipsoid body 382 that has a planar substantiallyoval-shaped bottom surface 383 that extends outwardly from either sideof the base 380 and forms a pair of upwardly extending arms 384 thatsupport an integral substantially U- or saddle-shaped portion 385 thatextends between the arms 384 and over the base 380. Each of the arms 384and the saddle 385 terminate at substantially planar, parallel uppersurfaces or strips 386. The arms 384 are sized and shaped to fit betweenthe saddle surfaces 346 of the compression insert 214 with the bottomsurface 383 being seated on the surface 347 of the compression insert214. The saddle further includes an under surface 387 and opposed,parallel substantially planar outwardly facing side surfaces 388 thatrun substantially perpendicular to the upper surfaces 386. As best shownin FIG. 19, a longitudinal connecting member seating surface 389 of thesaddle 385 further includes an elevation or rounded ridge 390 thatcurves upwardly from each of the side surfaces 388 and is at a highestelevation thereof substantially centrally located between the sidesurfaces 390, allowing for some angular motion of the connecting memberor rod 221 in the sagittal plane when the assembly 201 is fullyassembled with the rod 221 and implanted in a patient's spine along withat least one other bone anchor. Thus, with particular reference to FIG.25, in operation, both the convex surface 390 of the insert 216 and theconvex surface 368 of the closure top 218 engage the rod 121 at thesurface 222, with a degree of angulation of the rod 221 shown in phantomand identified as 221′.

In use, the shank 204, the retainer pieces 212 and the compressioninsert 214 of the assembly 201 are assembled in a manner identical orsubstantially similar to the manner of assembly previously describedherein with respect to the shank 4, retainer pieces 12 and compressioninsert 14 of the assembly 1. The assembled shank 204, retainer 212 andcompression insert 214 are then implanted on a human spine in a manneridentical or substantially similar to the manner previously describedherein with respect to the assembly 1. The screw driver is removed andthe receiver can be angulated with respect to the shank. Prior toinsertion of the rod 221 into cooperating bone screw receivers 210, anoptional pivot insert 216 can be inserted into the U-shaped channel 264of each of the receivers 210 and then into each compression insert 214with the arms 384 of the pivot insert 216 aligned with the arms 344 ofthe pressure insert 214, the arms 384 being received between the pair ofsaddle surfaces 346 until the planar surface 383 of the pivot insert 216seats on the planar surface 347 of the compression insert 214 and thecylindrical base 380 of the pivot insert 216 is received within theinner cylindrical surface 341 of the compression insert 214.

With particular reference to FIGS. 24 and 25, the rod 221 is eventuallypositioned in an open or percutaneous manner in cooperation with the atleast two bone screw assemblies 201. Optional (elastic) sleeves on therod can be used between the assemblies 201. Alignment of the rod surface222 with the saddle surfaces 346 of the insert 214 is initially providedand then maintained by the previously crimped walls 278 of the receiver210. The closure structure 218 is then inserted into and advancedbetween the arms 262 of each of the receivers 210. The closure structure218 is rotated, using a tool engaged with the inner drive 366 until aselected pressure is reached at which point the rod 221 is capturedbetween the saddle surfaces 346 of the compression insert 214, and insome embodiments, frictionally engages both the curved surface 390 ofthe pivot insert seating portion 389 and the convex surface 368 of theclosure top 218. In other embodiments, the rod 221 can be captured, butnot locked in place. Also, as the closure structure 218 rotates andmoves downwardly into the respective receiver 210, the rim 370frictionally engages the top surfaces 345 of the arms of the compressioninsert 214. Thus, in this embodiment, the closure top 218 pressesagainst and biases the rod 21 into engagement with the pivot insert 216that in turn presses against the compression insert 214 and the closuretop 218 also presses directly against the insert 214 to securely lockthe polyaxial mechanism of the assembly 201 by fixing the shank 204 andthe retainer 212 in a selected, rigid position relative to the receiver210. At this time it is also possible for the retainer 212 to expandsomewhat for an even tighter fit in the receiver cavity lower seat 294.

If removal of the rod 221 from any of the bone screw assemblies 201 isnecessary, or if it is desired to release the rod 221 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 366 on the closure structure218 to rotate and remove such closure structure from the cooperatingreceiver 210. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

It is noted that the bone screw components of the assemblies 1, 1′ and201 according to the invention previously described herein are typicallymade from a variety of materials, most typically metal and metal alloysincluding but not limited to stainless steel, titanium, and titaniumalloys. A desirable material that provides for low wear debris, adesirable coefficient of friction and good fatigue resistance for therod 221, for example, is cobalt chrome. Particularly if the rod 221 usedwith the assembly 201 is made from cobalt chrome, it is desirable forthe pivot insert 216 and the closure surface 368 that engage the rod 221to also be made from cobalt chrome. However, cobalt chrome is notnecessarily well suited for closure top and receiver components of theinvention due to its hardness. With reference to FIGS. 26 and 27, atwo-part or piece closure 218′ is illustrated wherein a domed bottomsurface portion 368′ is separate from a remainder of the closure 218′.Thus, the domed bottom surface 368′ may advantageously be made from afirst material, such as cobalt chrome, and a remainder of the closure218′ may advantageously be made from a second material, such asstainless steel or titanium.

The alternative closure top 218′ shown in FIGS. 26 and 27 may be analternative or substitute for the top 218 of the assembly 201 of theinvention. The top 218′ includes a body portion 361′ having a guide andadvancement structure 362′, a top surface 364′, an internal drive 366′,and a bottom rim 370′ substantially similar to the guide and advancementstructure 362, top surface 364, internal drive 366 and bottom rim 370 ofthe closure top 218 previously described herein with respect to theassembly 201. The closure top 218′ further includes a separate ordistinct bottom cap 371′ having the domed bottom surface portion 368′.The bottom cap 371′ further includes a neck 372′ with an end surfaceportion 373′ that is pressed upwardly into a small through bore 374′ ofthe body portion 361′ that communicates with the internal drive 366′until the end surface 373′ is fully within a space formed by such drive366′. Thereafter, the end surface 373′ or neighboring surfaces of thebody portion 361′ that form the bore 374′ may be worked so as tosecurely capture the neck end portion 373′ within the drive, forexample, shown as an enlarged or lipped domed end surface 373′ in FIG.27. As illustrated, the bottom cap 371′ further includes an upper convexspherical surface 375′ that is closely received by a lower concavespherical surface 376′ of the body portion 361′, the surface 376′ beingdisposed within and above the rim 370′. Thus, the lipped or otherwiseenlarged end portion 373′ of the neck 372′ is held within the internaldrive 366′ of the body portion 361′ by such lip and cannot slip throughthe smaller through bore 374′, with the spherical surface 375′ beingheld fully and securely against the spherical surface 376′. When the rod221 is made from cobalt chrome, the pivot insert 216 and the bottom cap371′ of the closure top 218′ may also be made from cobalt chrome,advantageously providing cobalt chrome to cobalt chrome low frictionalinterfaces with the resultant good fatigue characteristics and desirablegood wear, low debris attributes, while at the same time retaining thefavorable features of mating titanium guide and advancement structuresbetween the closure top 218′ and the receiver 210.

With reference to FIGS. 28-47, a third embodiment of a polyaxial bonescrew according to the invention, generally 401, includes a shank 404having a body 406 and an upper portion 408, a receiver 410, a two-pieceretainer 412, a compression insert 414, a pivot insert 416 and a closurestructure or top 418 and is shown with a longitudinal connecting memberin the form of a rod 421 having a substantially cylindrical outersurface 422. The shank 404, retainer 412, compression insert 414, pivotinsert 416, closure top 418 and rod 421 are substantially similar inform, function and materials to the respective shank 204, retainer 212,compression insert 214, pivot insert 216, closure top 218 and rod 221previously described herein with respect to the assembly 201. However,some of the above-listed components of the assembly 401 include a fewadditional and/or alternative features. Therefore, each of the assemblycomponents shall be briefly described below.

With particular reference to FIGS. 28 and 43-47, the shank 404 isidentical or substantially similar in form and function to the shank 204previously described herein with respect to the assembly 201. Thus, theshank 404 includes a thread 424, a neck 426, a tip 428, a spherical body438 with an upper surface portion 440, a planar annular top 442, a lowersurface portion/seating surface 444, a shank neck portion 445, and aninternal drive 452 that are the same or substantially similar in formand function to the respective thread 224, neck 226, tip 228, sphericalbody 238 with upper surface portion 240, planar annular top 242, lowersurface portion/seating surface 244, shank neck portion 245, andinternal drive 252 of the shank 204 of the assembly 201.

With particular reference to FIGS. 28, 30-32 and 43-47, the receiver 410is substantially similar in form and function to the receiver 210previously described herein with respect to the assembly 201 with theexception of a feature for placement and holding of the compressioninsert 414 in a desired aligned orientation. Thus, the receiver 410includes a receiver base 460, a pair of upstanding arms 462, a U-shapedchannel 464, guide and advancement structures 472, apertures 474, outerarm surfaces 476, inner thin walls 478, a cavity or chamber 490, upperinner cylindrical walls 492, spherical seating surface 494, a neck 496and a lower exterior 498 that are the same or similar in form andfunction to the respective receiver base 260, pair of upstanding arms262, U-shaped channel 264, guide and advancement structures 272,apertures 274, outer arm surfaces 276, inner walls 278, cavity or camber290, upper inner cylindrical walls 292, spherical seating surface 294,neck 296 and lower exterior 298 of the receiver 210 of the assembly 201.

Furthermore, with particular reference to FIGS. 30-32, formed withineach of the substantially cylindrical surfaces 492 and located directlybeneath the guide and advancement structure 472 of both the arms 462 isa recess 480 partially defined by a rounded stop or abutment wall 482.As will be described in greater detail below, the cooperatingcompression insert 414 includes a cooperating structure 484 that extendsoutwardly from each arm thereof that abuts against the respectiveabutment wall 482 of each of the receiver arms, providing a centeringstop or block when the insert 414 is rotated into place in a clockwisemanner as will be described below.

With particular reference to FIGS. 28, 29 and 43-47, the two pieceretainer 412 is substantially similar in form and function to thetwo-piece retainer 212 previously described herein with respect to theassembly 201. Thus, the retainer 412 includes a first piece 501 and asecond piece 502 having respective outer spherical surfaces 504 and 505,respective top surfaces 507 and 508, respective inner spherical surfaces514 and 515, respective inner frusto-conical surfaces 518 and 519 thatare the same or similar in form and function as the respective firstpiece 301, second piece 302, respective outer spherical surfaces 304 and305, respective top surfaces 307 and 308, respective inner sphericalsurfaces 314 and 315 and respective frusto-conical surfaces 318 and 319of the retainer 212 of the assembly 201, as well as all other featuresthereof. Furthermore, formed in each of the top surfaces 507 and 508 arerespective curved notches 522 and 523. The notch 522 is located near anend wall 532 of the piece 501 and the notch 523 is located near an endwall 534 of the piece 502. In operation, the notches 522 and 523 aredisposed opposite one another. The notches 522 and 523 are eachsubstantially U- or C-shaped and extend between inner and outerspherical surfaces of the respective pieces 501 and 502. The notches 522and 523 provide clearance during assembly and, if needed, disassembly ofthe pieces 501 and 502 about the shank upper portion 408 within thereceiver 410.

With particular reference to FIGS. 33-35 and 41-44, the compressioninsert 414 is substantially similar in form and function to the insert214 previously described herein with respect to the assembly 201. Thus,the insert 414 includes a cylindrical inner surface 541, an innerspherical surface 542, a pair of spaced opposed arms 544 having topsurfaces 545, a pair of saddle shaped surfaces 546, a lower planarsurface 547, inner planar arm surfaces 548, a saddle lower seat 550, afrusto-conical bottom surface 552, outer arm surfaces 555, each having agroove or depression 556 that are substantially similar in form andfunction to the respective cylindrical inner surface 341, innerspherical surface 342, pair of spaced opposed arms 344 having topsurfaces 345, pair of saddle shaped surfaces 346, lower planar surface347, inner planar arm surfaces 348, saddle lower seat 350, bottomsurface 352 and outer arm surfaces 355, each having a groove ordepression 356 previously described herein with respect to the assembly201. Like the assembly 201, the compression insert 414 of the assembly401 engages the pivot insert 416 at the planar surface 545, with thecylindrical surface 541 receiving a portion of the pivot insert 416 aswill be discussed in greater detail below. Unlike the insert 214, theinsert 414 planar seating surface 547 is slightly larger andsubstantially rectangular, providing greater surface contact with thepivot insert 416 and better access to tools if the pivot insert 416needs to be removed, with the pivot insert 416 also including structurefor manipulation thereof as will be described in greater detail below.

With particular reference to FIGS. 28 and 43-47, the closure top 418 issubstantially similar in form and function to the top 218 previouslydescribed herein with respect to the assembly 201. Thus, the closure top418 includes a guide and advancement structure 562, a top surface 564,an internal drive 566, a domed shaped bottom surface 568 and a bottomrim 570 that is identical or substantially similar in form and functionto the respective guide and advancement structure 362, the top surface364, the internal drive 366, domed bottom surface 368 and the bottomannular planar rim surface 370 of the closure top 218 previouslydescribed herein with respect to the assembly 201. As shown, forexample, in FIG. 42, the closure top 418 is sized and shaped so that thebottom rim 570 directly frictionally engages the top surface 545 of thecompression insert 414, pushing the insert 414 in a direction toward thereceiver base 460 so that the insert 414 directly frictionally engagesthe shank upper portion 408 at the spherical surface 440 pushing theshank 404 downwardly and thus pressing the retainer pieces 412 intofrictional engagement with the receiver spherical seat 494. Therefore,locking of the polyaxial mechanism is not dependent upon the closure top418 pressing on the rod 421 that in turn places force on the compressioninsert 414 into engagement with the shank 404. The closure top 418 mayalso be replaced by the closure top 218′ in some embodiments,particularly if the rod 421 is made from cobalt chrome and therefore thedomed bottom surface 368′ may also be made from cobalt chrome while theremainder of the closure top may be made from a different material.

With particular reference to FIGS. 28 and 36-47, the illustrated pivotinsert 416 is substantially similar in form and function to the pivotinsert 216 previously described herein with respect to the assembly 201.Thus, the pivot insert 416 includes a lower spherical surface 579, acylindrical base 580, a bottom rim 581, a body 582, a body bottomsurface 583, a pair of opposed arms 584, a saddle 585, planar arm topsurfaces 586, opposed side surfaces 588, and a saddle seating surface589 having an elevated portion or ridge 590 that is substantiallysimilar in form and function to the respective lower spherical surface379, cylindrical base 380, bottom rim 381, body 382, body bottom surface383, pair of opposed arms 384, saddle 385, planar arm top surfaces 386,opposed side surfaces 388, and saddle seating surface 389 having anelevated portion or ridge 390 of the pivot insert 216. Unlike the pivotinsert 216, the body 582 is of substantially rectangular cross-sectionas compared to the ovoid shape of the body 382 of the insert 216. Thesaddle 585 is also completely incorporated into the body 582 and fullyintegral and supported thereby. Furthermore, formed in the body 582 ateach of the side surfaces 588 is a through-groove 592 that runssubstantially parallel to the rectangular bottom surface 583 of the body582. The through-grooves 592 are somewhat U-shaped and are carved moredeeply into the side surfaces 588 in a direction of the top surfaces586, providing a hook-like surface for a manipulation tool (not shown)to easily grasp the insert 416 during assembly, and if needed, duringdisassembly of the pivot insert 416 from the assembly 401.

In use, the shank 404, the retainer pieces 412 and the compressioninsert 414 of the assembly 401 are assembled in a manner identical orsubstantially similar to the manner of assembly previously describedherein with respect to the shank 4, retainer pieces 12 and compressioninsert 14 of the assembly 1. Furthermore, the compression insert 414protruding arms structures 484 are frictionally mated with the receiverwall surfaces 482 as follows: After top loading of the compressioninsert 414 into the receiver 410 through the U-shaped channel 464, withthe arms 544 being located between the arms 462 during insertion of theinsert 414 into the receiver 410, the insert 414 is lowered until theinsert 414 is generally below the guide and advancement structures 472.The insert 414 is then rotated in a clock-wise direction into placeabout receiver 410 axis until the arms 544 are directly below the guideand advancement structures 472 and the protruding structures 484 abutagainst the rounded abutment walls 482 defining the receiver innerrecesses 480. With particular reference to FIG. 44, after the insert 414is rotated into such position, a tool (not shown) may be inserted intothe receiver apertures 474 to press the thin receiver walls 478 into theinsert grooves 556. The receiver 410 fully receives the compressioninsert 414 and blocks the structure 414 from spreading or splaying inany direction.

The assembled shank 404, retainer 412 and compression insert 414 arethen implanted on a human spine in a manner identical or substantiallysimilar to the manner previously described herein with respect to theassembly 1. Prior to insertion of the rod 421 into cooperating bonescrew receivers 410, a pivot insert 416 is inserted into the U-shapedchannel 464 of each of the receivers 410 and then into each compressioninsert 414 with the arms 584 of the pivot insert 416 aligned with thearms 544 of the pressure insert 414, as shown for example, in FIGS. 41and 42, the arms 584 being received between the pair of saddle surfaces546 until the body 582 bottom planar surface 583 of the pivot insert 416seats on the planar surface 547 of the compression insert 414 and thecylindrical base 580 of the pivot insert 416 is received within theinner cylindrical surface 541 of the compression insert 414.

With particular reference to FIGS. 43 and 47, the hard, inelastic,substantially non-deformable rod 421 is eventually positioned in an openor percutaneous manner in cooperation with at least two bone screwassemblies 401. Alignment of the rod surface 422 with the saddlesurfaces 546 of the insert 414 is initially provided and then maintainedby the frictionally mated surfaces 482 and 484 as well as by the crimpedwalls 478 of the receiver 410. The closure structure 418 is theninserted into and advanced between the arms 462 of each of the receivers410. The closure structure 418 is rotated, using a tool engaged with theinner drive 566 until a selected pressure is reached at which point therod 421 is captured between the saddle surfaces 546 of the compressioninsert 414 and frictionally engages both the curved elevated surface 590of the pivot insert seating portion 589 and the convex surface 568 ofthe closure top 418. Also, as the closure structure 418 rotates andmoves downwardly into the respective receiver 410, the rim 570frictionally engages the top surfaces 545 of the arms of the compressioninsert 414. Thus, the closure top 418 presses against and biases the rod421 into engagement with the pivot insert 416 that in turn pressesagainst the compression insert 414 with the closure top 418 alsopressing directly against the insert 414 to securely lock the polyaxialmechanism of the assembly 401 by fixing the shank 404 and the retainer412 in a selected, rigid position relative to the receiver 410. At thistime it is also possible for the retainer 412 to expand somewhat for aneven tighter fit in the receiver cavity lower seat 494. With referenceto FIGS. 45-47, it is also noted that in certain angular configurationsof the shank 404 with respect to the receiver 410, the pivot insertspherical surface 579 also frictionally engages the shank upperspherical surface 440 when the rod 421 presses downwardly upon the pivotinsert 416 due to downward force placed upon the rod 421 by the closuretop 418.

Also with reference to FIGS. 45-47 various degrees of rod 421 angulationor toggle are shown. Specifically, FIGS. 45-47 illustrates variousdegrees of angulation in the sagittal plane of a 5.0 mm rod held betweenthe pivot insert 416 curved surface 590 and the closure top 418 domedbottom surface 568. In particular, FIG. 45 illustrates no or zerodegrees of angulation in the sagittal plane; FIG. 46 illustrates a rodangulation or toggle of three degrees and FIG. 47 illustrates a rodangulation or toggle of six degrees. Thus, the bone screw assembly 401(as well as the bone screw assembly 201) advantageously provides for asemi-constrained, dynamic relationship between a non-deformable, hardrod and a polyaxial bone screw implanted in a human spine. Although therod 421 is securely captured to the bone screw assembly 401 within thereceiver 410, the rod 421 is free to move in the sagittal plane, beingallowed an operative limited toggling or angulation in such plane. Therod can also be surrounded by a spacer which can abut up against thereceivers and cooperate with the components to provide for dynamicspinal stabilization.

If removal of the rod 421 from any of the bone screw assemblies 401 isnecessary, or if it is desired to release the rod 421 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 566 on the closure structure418 to rotate and remove such closure structure from the cooperatingreceiver 410. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

Bone screw assemblies according to the invention may also be used in anon-angulating, fully constrained or fixed manner with a hard,non-deformable rod, for example, when fusion is desired. With particularreference to FIGS. 48-50, a larger diameter rod, such as the illustratedrod 421′ having an outer cylindrical surface 422′ may be substituted forthe rod 421 and used with the assembly 401 without the pivot insert 416and with a different closure top 418′. Thus, in FIGS. 48-50, theresultant slightly different assembly is identified with the referencenumeral 401′. The assembly 401′ therefore includes the shank 404, thereceiver 410, the two-piece retainer 412 and the compression insert 414all previously described herein with respect to the assembly 401. Theinsert 414 is advantageously sized and shaped to closely receive theslightly larger diameter rod 421′ as well as the rod 421 previouslydescribed herein. Specifically, the rod 421 illustrated with theassembly 401 has a diameter of 5 mm while the rod 421′ illustrated withthe assembly 401′ has a diameter of 5.5 mm.

The closure top 418′ is sized and shaped to mate with the receiver 410at the guide and advancement structures 472, similar to the closure top418 and only differs from the closure top 418 with respect to the sizeand surface features at a base thereof. Thus, the closure top 418′includes a guide and advancement structure 562′, a top surface 564′, aninternal drive 566′ and a bottom rim 570′ that is the same orsubstantially similar to the respective guide and advancement structure562, top surface 564, internal drive 566 and bottom rim 570 of theclosure top 418. In lieu of the domed bottom surface 568 of the closure418, the closure top 418′ includes a planar bottom surface 567′,downwardly extending rim 568′ and downwardly extending point 569′. Therim 568′ and point 569′ are sized and shaped for engaging andpenetrating the rod surface 422′ as best illustrated in FIG. 50.

With reference to FIGS. 51-61, polyaxial bone screw assemblies accordingto the invention may also be used with softer, deformable and/or elasticlongitudinal connecting members. The reference numeral 601 identifiessuch an assembly that includes the shank 404, the receiver 410, thetwo-piece retainer 412 and the compression or pressure insert 414 allpreviously described herein with respect to the assembly 401. Theassembly 601 further includes a deformable and/or elastic pressure pad616 and a closure structure or top 618 and is shown with a rod 621 madefrom a deformable material, for example, polyetheretherketone (PEEK).The pressure pad 616 may also be made from a non-metal material, such asPEEK. Both the pressure pad 616 and the rod 621 may be made fromsuitable plastic polymers, including, but not limited toultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites, including composites containing carbon fiber, natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers. The pressure pad 616 fits within a portion of thecompression insert 414 in a manner similar to the previously describedpivot insert 416 of the assembly 401. However, the pressure pad 616 doesnot include an elevated seating portion or ridge. Rather, theillustrated pad 616 includes a substantially solid U-shaped seatingsurface that is preferably operationally located flush with or slightlyabove the U-shaped surfaces of the insert 414, the pad 616 functioningto cushion and closely and evenly hold the deformable rod 621 inposition, the pad 616 also deforming, if needed, to provide suchcushioning without causing undesirable deformation and stress on the rod621 at the location where such rod is being held in place by the insert414.

The closure top 618 is substantially similar in form and function to thetop 418 previously described herein with respect to the assembly 401with the exception that a bottom domed surface thereof includes acentral projection and the domed surface and projection cooperate tofirmly press against the deformable rod 621 and fix such rod in positionwithout angular movement of the rod with respect to the closure top 618.Thus, the closure top 618 includes a guide and advancement structure662, a top surface 664, an internal drive 666 a domed bottom surface 668and a bottom rim 670 that are identical or substantially similar in formand function to the respective guide and advancement structure 562, topsurface 564, internal drive 566, bottom domed surface 568 and bottomannular planar rim surface 570 of the closure top 418 previouslydescribed herein with respect to the assembly 401. The domed surface 668further includes a centrally located downwardly directed projection inthe form of a somewhat rounded point 671. As shown, for example, inFIGS. 60 and 61, the closure top 618 is sized and shaped so that thebottom rim 670 directly frictionally engages the top surface 545 of thecompression insert 414, pushing the insert 414 in a direction toward thereceiver base 460 so that the insert 414 directly frictionally engagesthe shank upper portion 408 at the spherical surface 440 pushing theshank 404 downwardly and thus pressing the retainer pieces 412 intofrictional engagement with the receiver spherical seat 494. Therefore,locking of the polyaxial mechanism is not solely dependent upon theclosure top 618 pressing on the deformable rod 621 that in turn pressesthe pressure pad 616 and the compression insert 414 into engagement withthe shank 404.

With particular reference to FIGS. 54-58, the illustrated pressure pad616 is sized and shaped to be received by and downloaded into thereceiver 410 at the upper opening thereof, followed by insertion intothe previously inserted compression insert 414. The pressure pad 616 hasan operational central axis that is the same as the central axis of thereceiver 410 and the compression insert 414. A concave, substantiallyspherical bottom surface 679 of the pressure pad 616 has a radius thatis substantially the same or only slightly larger than the radius of thespherical body 438 of the upper portion 408 of the shank 404 and alsosubstantially the same as the compression insert spherical surface 542,the surface 679 being sized and shaped to be slightly spaced from orslidingly receive the upper surface portion 440 of the spherical body438 when the pressure pad 616 is seated within the compression insert414 and before any downward pressure is placed on the pad 616 by the rod621. The concave surface 679 partially defines an otherwisesubstantially cylindrical base 680 of the pressure pad 216, the base 680including an annular bottom rim surface 681 disposed about the sphericalsurface 679. The base 680 is sized and shaped to be received within theinner cylindrical surface 541 of the compression insert 414. The base680 is integral with an upper body portion 682 that has a planarsomewhat rectangular-shaped bottom surface 683 that extends outwardlyfrom either side of the base 680 and also forms a pair of upwardlyextending arms 684. The upper body portion 682 further includes aU-shaped or saddle-like seating surface 685 spanning between the arms684. Each of the arms 684 and the saddle seating surface 685 terminateat substantially planar, upper surfaces or strips 686. The arms 684 aresized and shaped to fit between the saddle surfaces 546 of thecompression insert 414 with the bottom surface 683 being seated on thesurface 547 of the compression insert 414. On either side of the saddleseating surface 685, the pressure pad upper body portion 682 is definedby opposed, slightly concave side surfaces 688, the surfaces 688 slopingslightly inwardly toward the cylindrical base 680 and then outwardly atthe arms 684. A pair of opposed grooves 692 are formed in the saddlesurface 685 and run through the arms 684 at a location centrally betweenand substantially parallel to the side surfaces 688. The illustratedgrooves 692 have a dove-tail shape, allowing for ease of use bymanipulation tools (not shown) for placement of the pressure pad 616within the compression insert 414 (see FIGS. 52 and 53) and fordisassembly therefrom, if needed.

In use, the shank 404, the retainer pieces 412 and the compressioninsert 414 of the assembly 601 are assembled in a manner identical orsubstantially similar to the manner of assembly previously describedherein with respect to the shank 4, retainer pieces 12 and compressioninsert 14 of the assembly 1. The assembled shank 404, retainer 412 andcompression insert 414 are then implanted on a human spine in a manneridentical or substantially similar to the manner previously describedherein with respect to the assembly 1. Prior to insertion of the rod 621into cooperating bone screw receivers 410, a pressure pad 616 isinserted into the U-shaped channel 464 of each of the receivers 410 andthen into each compression insert 414 with the arms 684 of the pressurepad 616 aligned with the arms 544 of the pressure insert 414, the arms684 being received between the pair of saddle surfaces 546 until theplanar surface 683 of the pressure pad 616 seats on the planar surface547 of the compression insert 414 and the cylindrical base 680 of thepressure pad 616 is received within the inner cylindrical surface 541 ofthe compression insert 414.

With particular reference to FIGS. 59-61, and also with reference toFIGS. 62 and 63, the deformable rod 621, illustrated as a 5.5 mmdiameter PEEK rod, is eventually positioned in an open or percutaneousmanner in cooperation with the at least two bone screw assemblies 601.Alignment of the rod surface 622 with the saddle surfaces 546 of theinsert 414 is provided by the frictional mating relationship between thereceiver rounded wall 482 and the protruding wall 484 of the compressioninsert 414 and then further aided by the crimped walls 478 of thereceiver 410. The closure structure 618 is then inserted into andadvanced between the arms 462 of each of the receivers 410. The closurestructure 618 is rotated, using a tool engaged with the inner drive 666until a selected pressure is reached at which point the rod 621 iscaptured between the saddle surfaces 546 of the compression insert 414and frictionally engages the saddle surface 685 of the pressure pad 616with the closure top projection 671 and at least a portion of the domedsurface 668 engaging the rod surface 622. The pressure pad 616advantageously deforms and conforms to the rod surface 622, providing asecure, non-slip surface therebetween. The pad 616 cylindrical surface680 that is received within the cylindrical surface 541 of thecompression insert 414 also provides a secure non-slip engagementbetween the pad 616 and the insert 414. As the closure structure 418continues to rotate and move downwardly into the respective receiver410, the rim 670 frictionally engages the top surfaces 545 of the armsof the compression insert 414, the insert 414 pressing against the shankupper domed surface 440, the shank pressing against the retainer pieces412 and the retainer pieces frictionally engaging the receiver at theseating surface 494 to securely lock the polyaxial mechanism of theassembly 601 by fixing the shank 404 and the retainer 412 in a selected,rigid position relative to the receiver 410. The torque required tosecure the polyaxial mechanism does not cause undue deformation to therod 621 due to the advantageous cushioning provided by the deformablepressure pad 616. Furthermore, the compression insert 414 is not twistedout of alignment due to the secure, close engagement between thecompression insert protruding surfaces 484 and the retaining walls 482of the recesses in the receiver 410. At this time it is also possiblefor the retainer 412 to expand somewhat for an even tighter fit in thereceiver cavity lower seat 494.

If removal of the rod 621 from any of the bone screw assemblies 601 isnecessary, or if it is desired to release the rod 621 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 666 on the closure structure618 to rotate and remove such closure structure from the cooperatingreceiver 410. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

With particular reference to FIGS. 62 and 63, it is noted that adeformable or elastic rod 621 according to the invention mayadvantageously cooperate with an elastic or inelastic spacer 696slidingly received about the rod 621 and located between a pair of bonescrews 601, the illustrated spacer 696 being in contact with sidesurfaces of each of the illustrated bone screws 601. The illustratedspacer 696 is tubular having an outer cylindrical surface 697 and aninner cylindrical surface 698 forming a through bore sized and shaped toslidingly receive the rod 621 therethrough. The illustrated spacerincludes opposed side surfaces 699, one or both of which may becut-to-length by the surgeon for a desired close fit between the bonescrews 601. The spacer 696 may be compressed between the bone screws601, followed by tightening of the closure tops 618 onto the deformablerod 621. Spacers of the invention may take other shapes, including, butnot limited to other curved and polygonal shapes having substantiallycentral or off-set through bores for receiving the rod 621 therethrough.

With reference to FIGS. 64-70 an alternative mono-axial bone screwassembly according to the invention, generally 701 is illustrated. Theassembly includes a bone screw body 704 having a threaded shank 706integral or fixed to a head or receiver 710; a deformable pressure pad716; and a closure top 718, and further shown with a longitudinalconnecting member in the form of a deformable rod 721 having an outercylindrical surface 722. The illustrated deformable rod 721 for use withthe assembly 701 is similar in form, function and material as the rod621 previously described herein with respect to the assembly 601, beingpreferably cylindrical in shape and made from PEEK. It is noted however,that longitudinal connecting members made from other materials andgeometries and used with or without cooperating outer spacers may beused with assemblies 701 of the invention, the receiver 710 and pressurepad 716 having alternative inner geometries sized and shaped for closelyreceiving such longitudinal connecting members.

The shank body 724 is elongate, having a helically wound boneimplantable thread 724 extending from near a neck 726 located near thereceiver 710 to a tip 728 of the body 706 and extending radiallyoutwardly therefrom. During use, the body 706 utilizing the thread 724for gripping and advancement is implanted into a vertebra leading withthe tip 728 and driven down into the vertebra with an installation ordriving tool (not shown), so as to be implanted in the vertebra to nearthe neck 726.

The neck 726 extends axially upward from the shank body 706 to theintegral receiver 710. The shank body 706 shown in the drawings iscannulated, having a small central through bore 729 extending an entirelength of the shank body 706 along a central axis thereof from thereceiver 710 to the tip 728. The bore 729 provides a passage through theshank 704 interior for a length of wire (not shown) inserted into avertebra prior to the insertion of the shank body 706, the wireproviding a guide for insertion of the shank body 706 into a vertebra(not shown).

To provide a biologically active interface with the bone, the threadedshank body 706 may be coated, perforated, made porous or otherwisetreated. The treatment may include, but is not limited to a plasma spraycoating or other type of coating of a metal or, for example, a calciumphosphate; or a roughening, perforation or indentation in the shanksurface, such as by sputtering, sand blasting or acid etching, thatallows for bony ingrowth or on-growth. Certain metal coatings act as ascaffold for bone ingrowth. Bio-ceramic calcium phosphate coatingsinclude, but are not limited to: alpha-tri-calcium phosphate andbeta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate(Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite(Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, isdesirable as hydroxyapatite is chemically similar to bone with respectto mineral content and has been identified as being bioactive and thusnot only supportive of bone ingrowth, but actively taking part in bonebonding.

With particular reference to FIGS. 68-70, the receiver 710 includes abase 730 integral with a pair of opposed upstanding arms 732 defining asquared-off channel 733 between the arms 732 with an upper opening,generally 734, and a lower planar seat 735, the channel 733 having awidth for operably snugly receiving the rod 721 between the arms 732 atlower opposed substantially planar side surfaces 736. Each of the arms732 also has an interior surface that defines an inner cylindricalprofile that includes a partial helically wound guide and advancementstructure 738. In the illustrated embodiment, the guide and advancementstructure 738 is a partial helically wound interlocking flange formconfigured to mate under rotation with a similar structure on theclosure structure 718, as described more fully below. However, it isforeseen that the guide and advancement structure 738 couldalternatively be a square-shaped thread, a buttress thread, a reverseangle thread or other thread-like or non-thread-like helically wounddiscontinuous advancement structure for operably guiding under rotationand advancing the closure structure 718 downward between the arms 732.Run-out top surfaces 739 partially defined by the planar arm surfaces736 form a stop for the closure structure 718, providing a securemechanism for locking such closure 718 when used with deformablelongitudinal connecting members such as the rod 721.

An opposed pair of tool receiving and engaging apertures 744 are formedon outer surfaces 746 of the arms 732. The apertures 744 are used, forexample, with a driving tool (not shown) for rotating the bone screwbody 704 into a vertebra (not shown).

Communicating with the channel 733 of the receiver 710 is a chamber orcavity 750 defined by a substantially cylindrical inner surface 752 andan annular base 754 disposed substantially perpendicular to the innercylindrical surface 752. The cavity 750 also communicates with thecannulation bore 729.

The closure top 718 is substantially similar in form and function to thetop 618 previously described herein with respect to the assembly 601.Thus, the closure top 718 includes a guide and advancement structure762, a top surface 764, an internal drive 766 a domed bottom surface 768a bottom rim 770 and a bottom projection 771 that are identical orsubstantially similar in form and function to the respective guide andadvancement structure 662, top surface 664, internal drive 666, bottomdomed surface 668, bottom annular planar rim surface 670 and bottomprojection 671 of the closure top 618 previously described herein withrespect to the assembly 601. As shown, for example, in FIGS. 69 and 70,the closure top 718 is sized and shaped so that after the domed surface768 and projection 771 fully engage the deformable rod 721, the bottomrim 770 directly frictionally engages the surface 739 of the bone screwreceiver 710, locking the closure top 718 in place independently of therod 721. Therefore, locking of the closure top 718 is not solelydependent upon the closure top 718 pressing on the deformable rod 721.

With particular reference to FIGS. 64-68, the illustrated pressure pad716 is sized and shaped to be received by and downloaded into thereceiver 710 at the upper opening 734 thereof, followed by partialinsertion into the cavity 750. The pressure pad 716 is substantiallysimilar in form and function and made from materials similar to the pad616 previously described herein with respect to the assembly 601 withthe exception that the pad 716 has a planar bottom surface 779 in lieuof the spherical surface 679 of the pad 616. Thus, the pad 716 includesa cylindrical base 780, an upper body 782 with a substantially planarrectangular bottom surface 783, a pair of opposed arms 784, a saddleseating surface 785, planar arm top surfaces 786, opposed side surfaces788 and through grooves 792 that are the same or substantially similarin form and function to the cylindrical base 680, upper body 682 withsubstantially planar rectangular bottom surface 683, pair of opposedarms 684, saddle seating surface 685, planar arm top surfaces 686,opposed side surfaces 688 and through grooves 792 of the pressure pad616 of the assembly 601 previously described herein.

In use, the pressure pad 716 is assembled with the bone screw 704 byinserting the pad into the channel 733 of each of the receivers 710 andthen into each cavity 750 with the arms 774 of the pressure pad 716aligned with the arms 732 of the receiver 710 and the pad 716 moveddownwardly until the planar surface 783 of the pressure pad 616 seats onthe planar surface 735 of the receiver 710 and the cylindrical base 780of the pressure pad 716 is received within the inner cylindrical surface752 defining the receiver cavity 750 and the base 779 of the pad 716also seats upon or is disposed near the annular surface 754 of thereceiver 710. The assembled shank bone screw body 704 and pressure pad716 are then implanted on a human spine by rotation of the shank body706 into bone, preferably utilizing a guide wire (not shown) extendingthrough the cannulation bore 729, a driving tool (not shown) beingengaged with the apertures 744.

With particular reference to FIGS. 69 and 70, the deformable rod 721, iseventually positioned in an open or percutaneous manner in cooperationwith the at least two bone screw assemblies 701. The closure structure718 is then inserted into and advanced between the arms 732 of each ofthe receivers 710. The closure structure 718 is rotated, using a toolengaged with the inner drive 766 until a selected pressure is reached atwhich point the rod 721 engages the saddle surface 785 of the pressurepad 716 with the closure top projection 771 and at least a portion ofthe domed surface 768 engaging the rod surface 722. The pressure pad 716advantageously deforms and conforms to the rod surface 722, providing asecure, non-slip surface therebetween. As the closure structure 718continues to rotate and move downwardly into the respective receiver710, the rim 770 frictionally engages the stop top surfaces 739 locateddirectly below the guide and advancement structures 738, locking theclosure top 718 to the bone screw receiver 710 without causing unduedeformation to the rod 721 due to the advantageous cushioning providedby the deformable pressure pad 716.

If removal of the rod 721 from any of the bone screw assemblies 701 isnecessary, or if it is desired to release the rod 721 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) that mates with the internal drive 766 on the closure structure718 to rotate and remove such closure structure from the cooperatingreceiver 710. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A polyaxial bone screw assembly comprising: a) a shankhaving an elongate body and an upper portion, the body being configuredfor fixation to a bone, the shank supper portion having a lower neck andan upper region that extends radially outward from the neck and has alower semispherical surface; b) a receiver having a top portion and abase, the receiver top portion having an upper channel adapted toreceive a longitudinal connecting member, the base having an internalseating surface partially defining a cavity, the channel communicatingwith the cavity, the cavity communicating with an exterior of the basethrough an opening; the shank upper portion being received through theopening and positioned within the cavity; c) a retainer having an innersurface and an outer surface, the retainer inner surface configured tobe in pivotal engagement with the shank upper portion semisphericalsurface and the retainer outer surface configured to be in engagementwith the receiver seating surface when the retainer is captured betweenthe shank upper portion and the seating surface, the retainer preventingthe shank upper portion from passing through the receiver openingallowing the shank to move polyaxially relative to the receiver duringpositioning, the retainer includes two discrete portions that are notjoined together.
 2. The assembly according to claim 1 including: a) acompression insert disposed within the receiver, the insert being sizedand shaped to frictionally engage the shank upper portion.
 3. Theassembly according to claim 2 including: a) at least one of a pivotinsert and a compression pad located in a recess of the compressioninsert and having a surface adapted to engage a longitudinal connectingmember received in the channel.
 4. A polyaxial bone screw assemblycomprising: a) a shank having an elongate body and an upper portion, thebody being configured for fixation to a bone; b) a receiver having a topportion and a base, the receiver top portion having a channel adapted toreceive a longitudinal connecting member, the base having an internalseating surface partially defining a cavity, the channel communicatingwith the cavity, the cavity communicating with an exterior of the basethrough an opening; c) a retainer having an inner surface and an outersurface, the inner surface configured to be engagement with the shankupper portion and the outer surface configured to be in engagement withthe receiver seating surface when the retainer is captured between theshank upper portion and the seating surface, cooperating to prevent theshank upper portion from passing through the receiver opening; theretainer having two separate portions that are not physically joinedtogether but abut against each other and the shank; d) a compressioninsert disposed within the receiver and configured to frictionallyengage the shank upper portion and adapted to engage the connectingmember.
 5. A polyaxial bone screw assembly comprising: a) a shank havingan elongate body and an upper portion, the body being configured forfixation to a bone; b) a receiver having a top portion and a base, thereceiver top portion defining a channel to receive a longitudinalconnecting member, the base having an internal seating surface partiallydefining a cavity, the channel communicating with the cavity, the cavitycommunicating with an exterior of the base through an opening sized andshaped to upwardly load the shank upper portion through the opening; c)a retainer having an inner surface and an outer surface, the innersurface configured to be in engagement with the shank upper portion andthe outer surface configured to be in engagement with the receiverseating surface when the retainer is captured between the shank upperportion and the seating surface, the retainer preventing the shank upperportion from passing down through the receiver opening and the retainermoving with the shank in polyaxial rotation with respect to thereceiver; d) a compression insert disposed within the receiver theinsert sized and shaped to frictionally engage the shank upper portionat a location spaced from the retainer; e) a discrete compression padlocated in a recess of the compression insert and having a first surfaceengaging a longitudinal connecting member and an opposed second surfaceengaging the shank upper portion.
 6. A polyaxial bone screw assemblycomprising: a) a shank having an elongate body and an upper portion, thebody being configured for fixation to a bone; b) a receiver having a topportion and a base, the receiver top portion defining a channel toreceive a longitudinal connecting member, the base having an internalseating surface partially defining a cavity, the channel communicatingwith the cavity, the cavity communicating with an exterior of the basethrough an opening; c) a retainer having an inner surface and an outersurface, the inner surface configured to be in engagement with the shankupper portion and the outer surface configured to be in engagement withthe receiver seating surface when the retainer is captured between theshank upper portion and the seating surface, the retainer preventing theshank upper portion from passing down through the receiver opening andthe retainer moving with the shank in polyaxial rotation with respect tothe receiver; d) a compression insert disposed within the receiver, theinsert being sized and shaped to frictionally engage the shank upperportion; and e) a discrete compression pad located in a recess of thecompression insert and having a surface engaging a longitudinalconnecting member.